Shore crabs reveal novel evolutionary attributes of the mushroom body.

Nicholas Strausfeld,Marcel E Sayre

doi:10.7554/elife.65167

Abstract

Neural organization of mushroom bodies is largely consistent across insects, whereas the ancestral ground pattern diverges broadly across crustacean lineages resulting in successive loss of columns and the acquisition of domed centers retaining ancestral Hebbian-like networks and aminergic connections. We demonstrate here a major departure from this evolutionary trend in Brachyura, the most recent malacostracan lineage. In the shore crab Hemigrapsus nudus, instead of occupying the rostral surface of the lateral protocerebrum, mushroom body calyces are buried deep within it with their columns extending outwards to an expansive system of gyri on the brain's surface. The organization amongst mushroom body neurons reaches extreme elaboration throughout its constituent neuropils. The calyces, columns, and especially the gyri show DC0 immunoreactivity, an indicator of extensive circuits involved in learning and memory.

Highlights

Insect mushroom bodies, those of Drosophila, are the most accessible models for elucidating molecular and computational algorithms underlying learning and memory within genetically and connectomically defined circuits (e.g. Aso et al, 2014a; Senapati et al, 2019; Jacob and Waddell, 2020; Modi et al, 2020)
The final observations address the relationship of the mushroom body to the reniform body, a center common to malacostracan crustaceans
We have shown that the lateral protocerebrum is divided into a rostral and caudal part (RLPR and caudal volume of the lateral protocerebrum (CLPR)), the former containing the paired mushroom bodies

Summary

Introduction

Those of Drosophila, are the most accessible models for elucidating molecular and computational algorithms underlying learning and memory within genetically and connectomically defined circuits (e.g. Aso et al, 2014a; Senapati et al, 2019; Jacob and Waddell, 2020; Modi et al, 2020). Those of Drosophila, are the most accessible models for elucidating molecular and computational algorithms underlying learning and memory within genetically and connectomically defined circuits Because of the importance of mushroom bodies in understanding the relevance of synaptic organization in sentience and cognition, recognizing evolutionary divergence of these centers would be expected to yield experimentally testable predictions about evolved modifications of circuitry in relation to ecological demands imposed on the species. Insect mushroom bodies show a remarkably conserved organization, which makes them relatively unsuited for neuroevolutionary studies. Less attention has been given to neural arrangements comprising the mushroom body lobes (columns), some studies have addressed distinctions in basal groups such as silverfish (Zygentoma), dragonflies and mayflies (Farris, 2005; Strausfeld et al, 2009)

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